HI All,

Well, the XYL and I tried powering up the Predicta Holiday last night. Ramped the power up slow and got the tubes to glow. No sound or raster. Everything smelled and looked fine. Could hear a slight noise from the flyback and up at the CRT, a regular beat. Looking at the troubleshooting chart it says power supply is the most likely culprit. So I pulled the HV can off and measured the flyback for resistance. With the can off I can see a drip underneath the flyback.

5-D, 11.6 Ohm out of expected 12.
4-3, 10 Ohms out of expected 13
3-B, 8.6 out of expected 11
L17, spot on, 1.7 ohms

Although it says on the schematic not measure between 5 and the HV output, it gives an expected measurement of 385 ohms. I figured that the do not measure was for older VTVM's, so I checked it anyway, 366 ohms. So the top coil seems good, lower coil a little low in resistance. Shorted turns? When we pulled the HV rectifier tube, it was completely cool to the touch. With the really low filament voltage I am not sure how warm it should be.

So, any suggestions where to start?

Jonathan

Although it says on the schematic not measure between 5 and the HV output, it gives an expected measurement of 385 ohms. I figured that the do not measure was for older VTVM's, so I checked it anyway, 366 ohms. So the top coil seems good, lower coil a little low in resistance. Shorted turns? When we pulled the HV rectifier tube, it was completely cool to the touch. With the really low filament voltage I am not sure how warm it should be.


I'm pretty sure that warning means not to measure the voltage with the set powered up, because of the presence of high voltage spikes. There should be no harm in measuring the DC resistance when the set is powered down.

So, any suggestions where to start?

Measure the B+ voltage at the output of the rectifier, and on the various power supply rails? Fusible resistor OK?

With the horizontal output tube plate cap removed, is DC supply voltage present on the cap lead?

All those resistance readings are well within spec. Dripping wax is common and no cause for concern. When working normally, the flyback will be a little warm after maybe 30 minutes. Don't expect the set to work until you get to around 110 or more on your variac.

If your TV has all of its original capacitors, I'll put on my magical wizard hat and predict that you likely have a bad capacitor -- and more likely, a few dozen of them.

I wouldn't fret over the flyback at the moment. Some wax drip underneath it is common.

Many restorers would plunge ahead and start recapping, beginning with the (duh) electrolytic capacitors in the power supply. The schematic shows the voltages ("280V source" and so on) that the TV is supposed to produce downstream of the rectifiers and p-s filter caps. Set your variac at 117 volts and test those points.

Until your power supply is producing the basic voltages needed by the rest of the TV, trying to troubleshoot problems on a symptom-by-symptom basis can be frustrating and confusing.

What have you done to this TV up to this point? Tested tubes? Cleaned controls? It's helpful if you confine all discussion of your TV to one thread, so that people can read about it in context instead of searching around in multiple threads to get a clue about what's happening.

This article has some advice about basic first steps that may be useful:

http://antiqueradio.org/FirstStepsInRestoration.htm

If you have already done all of those good things, then recapping is next on the agenda. The only question is whether you want to do them all at once, or one-by-one (or few-by-few), powering up the TV periodically to see if you're making progress (or at least, not making things worse).

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Fusible resistor ok. Will check B+ and DC on the horiz. cap. I did bring the line voltage up to 117. I do feel silly for not doing a complete voltage check before posting. I'm sorry, my enthusiasm ran away with me.

Not much has been done, other than a good visual inspection and basic cleaning. I am going to jump into the recap, I gotten the list together and will be ordering that Monday. So, soon I will pull the PCB, replace all paper and electrolytics and measure all resistors and replace as needed. I'll test all the tubes, but I don't put that much faith in my cheapie Eico tester. I just got ants in my pants and wanted to see what it did as is. Since I am waiting on caps I'll poke around and check voltages.

Thanks for all the help! I'll try to take a deep breath and be more methodical.

Jonathan

If your TV has all of its original capacitors, I'll put on my magical wizard hat and predict that you likely have a bad capacitor -- and more likely, a few dozen of them.

I wouldn't fret over the flyback at the moment. Some wax drip underneath it is common.

Many restorers would plunge ahead and start recapping, beginning with the (duh) electrolytic capacitors in the power supply. The schematic shows the voltages ("280V source" and so on) that the TV is supposed to produce downstream of the rectifiers and p-s filter caps. Set your variac at 117 volts and test those points.

Until your power supply is producing the basic voltages needed by the rest of the TV, trying to troubleshoot problems on a symptom-by-symptom basis can be frustrating and confusing.

What have you done to this TV up to this point? Tested tubes? Cleaned controls? It's helpful if you confine all discussion of your TV to one thread, so that people can read about it in context instead of searching around in multiple threads to get a clue about what's happening.

This article has some advice about basic first steps that may be useful:

http://antiqueradio.org/FirstStepsInRestoration.htm

If you have already done all of those good things, then recapping is next on the agenda. The only question is whether you want to do them all at once, or one-by-one (or few-by-few), powering up the TV periodically to see if you're making progress (or at least, not making things worse).

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

Quite agree. I simply do not believe in powering up any radio or television receiver until ALL of the filter and paper capacitors--"all of them" being the operative-- have been replaced.

Did I mention all of them?? Powering up a receiver with original caps is in my very humble opinion, silky, lazy and risky. Heavy on the risky. Recapping your set fully will reduce risk tremendously. Then you can power it up and go looking for whatever else may be Ailing it, such as mica caps, resistor issues, etc.

Quite agree. I simply do not believe in powering up any radio or television receiver until ALL of the filter and paper capacitors--"all of them" being the operative-- have been replaced.

Did I mention all of them?? Powering up a receiver with original caps is in my very humble opinion, silky, lazy and risky. Heavy on the risky. Recapping your set fully will reduce risk tremendously. Then you can power it up and go looking for whatever else may be Ailing it, such as mica caps, resistor issues, etc.

It is not all that risky if you do the power up right. A slow start with a variac, the back off so any smoke or signs of trouble can be seen, and periodically feeling the cans and transformer to make sure they are not getting hot is about all that needs to be done to give a safe test power up. (and of course having the sense to pull the plug if signs of trouble manifest)

It is always good to have a baseline before you start changing caps so that if you screw it up you know to check your own work, and not simply blame the set and start chasing shadows.

Second part is true. However, why waste your time with components that everyone knows are kaput, or will soon be!

Just do it right the first time, be careful--don't rush--and more than likely you'll have a nice and SAFE set to tweak on the backend!

George

Anything newer than 1960 I power up replace what (if anything) is preventing it from working right and run it with as many original parts (including caps) as it will run properly with...If an original cap goes in the course of later use I find it change it, and return to using the set. Much of the fun is troubleshooting...Why waste it with a shotgun recap?

If your set is being used properly (with someone watching it at all times) if a lytic goes bad it will be noticeable and unless you let it run in that state for several minutes almost nothing ever gets damaged.

Your claim of fire, and danger rings of trumped up alarmism/over caution to me. I've seen several dozen caps that have gotten hot and puked their guts, but never any cap fire evidence....Hell some sets had problems with the power switches starting REAL house fires when the sets were new and NOBODY here changes a power switch unless it has failed. It's as goofy to me as saying we should gut all our sets and install flat panels cause someone might get hurt from a random CRT implosion. Life is all about calculated risk.

The HV rectifier tube won't get warm with the other tubes. The horizontal circuit and flyback have to be operating for the tube to even work. Normally, you won't even see the filament glowing on the HV rectifier when the set is running.

As an ex-firefighter, for me it is about the risk VS gain equation. Unfortunately I don't know enough in this situation to really asses the risks or mitigate the hazards. So I should be more cautious.

I'm putting together a parts list and I have a couple of questions. Looks like 1 watt metal oxides should fit for the 1/2 watt resistors. How often do these go bad? On a Hallicrafters SX-44 panadapter I did recently, 90% were bad. On an SX-43 they were pretty much all good. What are these Predictas like in that regard? I can order the exact values called for on the video PCB or buy a variety pack of values and see how it goes. Thoughts on that?

I'm not planning on messing with the tuner for starters, just the video board and all the paper and electrolytic caps under the chassis. I can't seem to find a PDF of the Philco manual anywhere. I saw that Phil had a PCB diagram with top and bottom views but mine is different. I'd love to have one of those.

I will keep this project in this thread to make it less confusing.

Thanks!

Jonathan

Edit: Bruce, thanks for the info. That's what I figured, with such a low filament voltage.

Video boards on predictas rarely have issues, no paper caps there, and resistor values are generally not critical. In fact most of the resistors can be off a lot and still be fine.

Generally speaking if you have a lot of exp with diagnostics you can get away with shot gun replacing. If not you are best to base line and then replace a few. Of course with a predicta pulling the PCB is a bit of a pita, but often you can just unstake the grounds and lift a few wires to get access.

I also like to base line a set to determine its overall status before touching it, and that includes cleaning it. I have gotten sets that's that were real dogs due to a single misplaced cap on a botched recap.

I have a series on a 10L chassis, there are several parts. You may find it interesting as I talk about my approach.

https://www.youtube.com/watch?v=PbKmydNJzg0

If you want to jump right to pulling the pcb ck part 5

You can find the Sams folder #439-1 at the early television web site. All the best,Tom

Dave, maybe I am mis-speaking. I mean the main PCB, which does have paper caps. I don't have any tv diagnostics experience at all. That is why I was trying to see what it would do as is, to get a baseline. Considering the PITA to get that PCB off though, shot-gunning might be called for.

Doing some more poking around I see the multi-tap sand resistor is waaaay off. The 8 ohm section reads 30. The 13 ohm section reads 62 and the 17 ohm section is reading 93! Furthermore, I have discovered that R76, the 400 cold, 11 ohm hot, has been replaced with a 10 ohm resistor. Yikes! What is the best modern replacement for that?

Thanks!

Jonathan

EDIT: Tom, thanks but I have the Sam's. It doesn't have the same PCB diagram that Phil had for his set from the Philco manual.

NTC thermistors are still made. Often referred to as "inrush current limiters". Digikey and others sell them.

N2IXK, I'm digging through Mouser and Digikey. Not quite sure, but I am looking for 10 ohms @ 25c? I'm assuming the 25C number has to be at operating temps. All that I see so far seem to have a very high B number, which I assume is the initial cold resistance? As long as the B is higher than 400 all that would mean is a longer start up time?

Thanks!

Jonathan

25C is roughly room temperature, or the "cold" resistance. The hot resistance is usually specified at a given current.

Thanks! Duh, did the conversion wrong. I'll keep digging through data sheets.

Jonathan

The highest I've seen is 220 ohms cold. I used two of them in series: http://www.mouser.com/search/ProductDetail.aspx?R=0virtualkey0virtualkeySL12-22101

Bob, thanks! The price is right too. Added 4 of them to the ever growing Mouser order. Also been watching your Holiday resto videos, very helpful and informative.

Dug up some power resistors out of the stash that will work for the multi-tap sand resistor. I'm kinda surprised that the value of that had drifted so high, I've never seen a power resistor drift so much. Are those wirewound?

At work for 48 hours but should have some time to replace the power resistor on Thursday. Didn't get the order in so no new parts bonanza arriving this week. The 21FAP4 will get here this week though. Fingers crossed it arrives intact! And that it will work on a Predicta. We shall see. I was thinking of cutting the CRT wires I need to be able to swap up near the socket and putting bullet connectors on them. That way I can test the 21FAP4 works but continue to use the one the set came with if it has any life.

Thanks all! Really appreciate all the help and advice.

Jonathan

EDIT: I didn't put a link for the bullet connectors, but there is an epay link to actual bullet connectors?

Yes, the tapped resistor is wirewound and I've seen them with increased resistance too. I noticed green corrosion on the leads and think that is the cause.

Interesting. No corrosion visible on mine. Might be internal though. I'll do an autopsy when I pull it out.

Jonathan

Moisture in the air makes those sand resistors corrode. They were never designed to last all these years, even not being used.

Removed the multi-tap power resistor and subbed in some replacements and bingo! We got a raster and a little sound. The picture was dim and the sounds was very low, mostly the occasional scratch. The picture got dimmer after a few minutes of operation. Still, progress! We now know we have something to work with. And it was cool to see the little dot in the center of the screen when we shut it off, haven't seen that in years!

The power resistor had no visible corrosion. I may smash it to see the insides, I am still surprised that it had drifted so far off.

Working on a parts list, digging through my stash to see what I have on hand. The 21FAP4 arrived intact and in the original box with the pin protector. It is supposed to be NOS and it looks like it. Once I get the set working properly we'll give that a test.

Bob, after watching more of your videos, I am leaning towards replacing all the resistors and couplates like you did. What do you thing of replacing the sockets out of hand? After watching the trouble they gave you I am quite tempted to do so.

As to the couplates, I was hoping I could ask you for part numbers for the components. In return, I would take detailed construction pictures and post them in a separate thread for easy location for others in the future.

Thanks for all the help folks!

Jonathan

You may find that the 12FAP4 that you have is perfectly good, and I hope you don't need the spare.

The capacitor replacements should make a big improvement in the image you see on that screen.

Bruce, I hope you are exactly right. While I haven't actually pulled the CRT housing off to verify what I have in there I think it is the original 2V filament, 21EAP4. So while there is still a chance it has life it is a little less likely.

Big ol' cap order on the way, along with some other parts, Novus polishes ect. Not everything I need by a long shot but enough to get to work while I figure out what else we need.

Jonathan

Hi All,

Rio and I got to a little work on the Predicta last night. We got the surge suppressors installed, gutted and stuffed one of the electrolytics and replaced a couple of paper caps. I am starting on the chassis side and will then go to the PCB. That will allow me to get familiar with the set and round up all the parts I will need to do the PCB.

The electrolytic was a nasty mess to take apart! It was hilarious seeing Rio's reaction to it. It was loaded with something that looked like a cross between something you find in an infant's diaper and lithium grease. Came apart pretty easily and went back together and looks good. Rio did a great job of peeling the rim back so we could pull the insides out. Of course, we are checking the resistors as we go along. Of the three resistors I have lifted and tested all three are off, 1k = 1.5k, 220k = 700k!, and a 18k = 15.2k. So, looks like ordering a complete resistor set is called for.

Overall, not a bad start. Should get some more time in over the weekend and get another parts order in on Monday. Fun stuff and good times. Thanks for all the help so far!

Jonathan

Hi All,

Busy week but still managed to get some work done on the Holiday. The bottom of the chassis is almost done. I re-stuffed the two electrolytics that mount on the bottom but used a terminal strip to mount the three to replace the top mount can. The can was too skinny and my caps too big, would have been a job to get it to fit. Since this picture I have done some more work, just on cap to replace and three resistors to check. I plugged it in and ramped it up with the variac and it still works but with the same dim, flashy raster and very little audio.

Next week I hope to pull the PCB and start on that, but it is going to be another busy week. Anyone who has made some couplates want to share their recipe? Bob's videos are very good but I am not quite sure what the best type of ceramic caps to order is.

So far so good! Thanks for all the help.

JOnathan

Anyone who has made some couplates want to share their recipe? Bob's videos are very good but I am not quite sure what the best type of ceramic caps to order is.

Only use C0G or NP0 ceramic. Other types drift with temperature. Use mica or plastic film is you can't get C0G in the value you need. I used mostly 630 volt, but a few 500 and 250 where I could get away with it. You should use a 1500 volt or better for the 1500pF cap in the vertical feedback network.

Bob, great and thanks. I'll get some ordered up this week. Drat, I ordered a 1kV cap for the cap (don't remember number, I'm at work) on the board that needs to match the cap on the vertical network. Oh well, I'll order another.

1kv is enough. I didn't have the schematic in front of me earlier.

I made a bunch of extra couplates. If you rather just get them from me, let me know.

Bob, I meant to mention that the odd ceramic tube cap that you thought might be a replacement in one of your videos was in my Holiday too, so it must have been a stock item. Strange kinda cap. Good that 1kV is enough. I'll send you a PM about the couplates.

Are 1n4007 diodes OK to replace the HVDC diodes? I hope so, I already soldered some in. :-)

Also, what value resistor to sub in for the CRT filament for testing purposes. Bob mentions it in one of his videos but I can't seem to find it.

Still chugging along. The container of replaced parts is getting full!

NEVER MIND: Found Bob's video that answered both of those questions, yes and 10 ohm.

1N4007 (rated for 1,000 volts @ 1 A) are fine but I've switched to beefier IN5408 ( 1,000 volts @ 3A) lately. I've heard some guys use two diodes in series for extra protecting in case one shorts. Seems like overkill but wouldn't hurt.

Use ohms law. Resistance = filament voltage / current = (2.35 or 6.3) volts / 0.6 A. Really though you don't need to be exact - something around 3.9 - 15 ohms is fine.

Hey Bob, thanks for the reply. I may order some 5408s, all I have on hand is 5406s. The 4007s will be good enough for testing purposes.

Hi All,

Well, a busy week here but still managed to get a lick in on the Predicta. I got the main PCB removed and started to remove and replace components. I am going with a blanket replacement of paper caps, couplates and resistors. I've come up with a few questions from the components values.

C25: Looks like a little resistor with two black bands. Sam's says it is a 1uF?! I must be reading that wrong, but it would seem that 1pF is the only other interpretation.

R49 and R52: R49 is a 3600 ohm. The notes says this goes with a PCB marked with a yellow dot. R52 is a 2.7mOhm and the notes says this goes with a PCB that has an orange dot. I see no dots on my PCB but I do see a green stripe. I'm guessing I should stick with the values that are in the board, but anyone have any insight?

Over all the board is in decent shape. I have one 7 pin socket that needs replacement. All the 9 pin sockets look OK. In my stash I found some PCB mount 9 pin sockets, one of which is the same make and number but appears a little later. The other ones I have are even cheaper looking than the originals. I'm not sure if I should replace all of them or just the borked one.

Jonathan

Sams says 1.0 mmfd for C25. That's short for micro micro Farad which is the same as pico Farad (pF).

I'd go with the resistor values currently in the board - especially if they look to be originals.

As for the tube sockets, if you stick with the originals be very gentle when inserting and removing tubes. The metal used is fairly thin and breaks easily.

OK, so what kind of cap is the 1pF? I am assuming it's a ceramic and hence no need to replace out of hand. Are these resistor looking caps common?

Thanks Bob! Also, I'm going to take you up on your offer to buy the couplates. I'll send you an email.

Jonathan

Yes, ceramic - no need to mess with it. You will mostly see these caps in tuners and other RF circuits where very small capacitance is needed.

So, I've been looking for sockets. I can't seem to find any that have the center solderable pin. I'm not sure how important that is, but some of the center pins have traces that meet up with component traces. Some of them are just little islands unto themselves. Lots of 7 and 9 pin ceramic sockets available but noe with center pins. Any oPINions on how important they are?

Jonathan

If the tube that goes in the socket don't have a center pin, and the tube is not in the IF or video stages the center pin is irrelevant...If it is in the IF or video it still may not matter, but those stages can be picky about capacitance changes that tiny redress (like removing that piece) can cause. If IF and video stages have working sockets I'd leave well enough alone.

Surplus Sales of Nebraska - scroll down and you'll find 7 and 9 pin that are perfect replacements -

https://www.surplussales.com/Tube-Sockets/TubeSkts-2.html

7-pin
(TUA) MSM-1441-200 or (TUA) 7P-CP - the shield is easy to remove if you don't need it.

9-pin
(TUA) 751V504C06

I think you'll find it helpful to read through other Predicta restoration threads where the same issues have come up before. Here's one of mine showing the new sockets.
http://www.videokarma.org/showthread.php?t=255328&page=3

Got some time in on the set this week. All parts that I had on hand have been mounted on the main PCB. Spent quite a bit of time cleaning all of the contacts on the board and the board itself. Did a lot of chassis cleaning. Ordered the remaining parts and some spare tubes, along with some replacement sockets. Ordered some Novus plastic polish. With any luck all should arrive next week.

I really can't wait to see a picture on this thing.

Jonathan

Well, the main PCB is done! Hopefully anyway. I bought a set of couplates from Bob and they look great! Really fine work. While I feel a little dirty for not making my own, Bob's look so good I'm glad I didn't. I can't seem to figure out the inline attachments but here is the main board.

I'm waiting for Rio to re-connect the board and test this thing out! I hope she knows what an act of love that is! The anticipation is killing me. Remember the Wide World of Sports intro? The thrill of victory or the agony of defeat! Which awaits me?

While I'm killing time waiting to find out, I have a radio shack RF modulator that I am playing with to see if I can come up with a way to see an image, assuming the thrill of victory prevails. I am guessing that the Predicta has a 300 ohm input and that I need the little balun to connect it. Is this correct? Is there anyway to whip up something, just to see if I can get any kind of image?

Thanks for all the help folks!

Jonathan

Looks good!
The 300ohm balun is advisable to use....If you lack one you could try hooking the center lead of the 75ohm coax up to either 300ohm lead and see if you have signal.

If there is a Radio Shack near you, they carry an over-built Balun/TV antenna matching transformer for ~$5 that should work nicely.

Located a balun. It is 20 miles away, one way. Luckily the XYL is going to town anyway. So that problem is solved.

However, I am wondering, should the RF modulator be powered from the same isolation transformer of the set? And if so, I'm guessing I should make sure the neutral is connected the same way on both? And what about the DVD player?

Tom, I am going to get a Blonder-Tongue modulator, but the rat shack one was free and fell in my lap. Good enough to see if I can get this set working. Then we'll work out a better quality system.

Thanks!

Jonathan

I'd keep only the set on the isolation transformer. The set should have isolation in it's internal antenna transformers, but some don't, and others the isolation sometimes fails.

The modern gear don't have hot chassis issues so it does not need an isolation transformer. The reason you isolate ONLY the TV's power input is so that it will play nice with the 'chassis ground' of ANY piece of gear you connect to it hot or cold. Also if you have recent test equipment like an o'scope NEVER plug BOTH the set and the scope into the SAME isolation transformer....If the scope is grounding to neutral and the TV chassis is grounding to hot, damage will occur the instant you ground the scope to the TV chassis to try to measure the TV with the scope.

Any working mod is good enough for testing in my book.

For example if you had 2 hot chassis sets one with +70volts chassis with respect to earth, and another with -98volts with respect to earth and you wanted to feed them with a cold chassis (0V with respect to earth) signal source. the signal source would get plugged into the wall, +70 would be pluged into isolation transformer #1 and -98 would be plugged into a second, different isolation transformer (#2). If you plug devices with different chassis voltages into the same outlet/source you CAN NOT directly connect them together without causing damage....If you did connect them it would be roughly equivalent of taking a household plug jumpering one prong to the other and then plugging it in!...(granted there are parts in the sets that tend to burnout before the breaker trips).

When in doubt measure voltages (AC and DC) between grounds and hot leads in signal wires you wish to connect (toggle power states on any hot chassis gear while measuring). If you see more than 5V think twice or consult someone.

You could just connect an antenna to the modulator and a antenna to the set. Put the modulator antenna near the tv antenna and tune the tv to the modulator channel. Not strong enough to transmit any distance, but I have used this setup to test sets before.

And it is... a drum roll please....

THE THRILL OF VICTORY!!

Well holy cow. The set actually works! The picture is dim and there is no sound, except hum. That may well be that the cheap rat shack modulator or HDMI to composite converter isn't working. I'll have to dig into that.

However, the pictures is dim. Part of it that the inside of the cover is filthy. Even so, it should be brighter. I have read about cooking the filament a little to help bring the tube back to life, any recommended voltages and duration? I am planning on removing the shroud today and cleaning the screen and at that point I should know for sure which tube it is, although it must be one of the 2.35V tubes. And I do have a 21FAP4 NIB but I'd like to see what can be done with the original tube first.

Overall, what a wild success! The controls seem to work ok, horizontal hold locks in. Picture is poorly focused and needs some shaping. But I did watch an episode of Peter Gunn on it! Although with the sound coming out of the computer.

Thanks SO MUCH folks! Never, ever could have gotten it to here without the help I have kindly received on this forum.

Jonathan

Great! I'd check the voltages at the CRT socket against what is called for in the schematic, measure the HV, and test the CRT before trying to cook the CRT. Dimness can be gun bias circuit problems, low HV, or a weak electron-gun. Knowing which will give you a path to the most effective solution.

IIRC my B&K 466 has in it's instruction manual a 'cooking proceedure' that states to multiply the designed heater voltage by 1.4 and let it sit that way for 5-25 min (I've gone longer on hard luck cases)....That works best in test mode with it reading emission (at least with my rig).

I'd limit possible causes to a weak gun before cooking it, and I'd verify tube number and designed heater voltage before trying to test or cook it.

Tom, I don't have a CRT tester as yet. How can I test the HV? I do have a HV probe for a voltmeter but haven't used it in a long time and IIRC it would load a flyback down too heavily.

I'm going to get the shroud off and find out which tube we are dealing with and take what voltage measurements I can.

Jonathan

You need a HV probe or HV meter. You want a HV probe good to at least 20KV (30-40KV is better especially if you plan to do color work).
I'm not sure where you came up with the notion that your probe will load it too heavily....If it is designed for 15-20KV duty it should be fine....Most HV meters TV techs used were essentially an HV probe with a volt meter tacked on... Look at the HV spec on the schematic and select a probe that can do about 5KV or more above that number.

You should be able to find a half decent CRT tester for $10-$50...I got my trusty B&K 466 for $25 working.

Compare neck voltages with schematic bearing in mind that some vary with control settings, and those settings are often noted on the schematic.

OK, we are dealing with a 21EAP4. Looking at voltages:

B+ = 273, should be 290
Pins 2&6 of CRT, 405 should be 420
pin 7 of CRT, 27 should be 35
Filament = 2.28VAC
HV = 14.4kV, should be between 14 and 15.5kV
e
I do hear some crackling/popping down in the well of the HV rectifier. Should get some dielectric grease in there. Not sure what my HV probe is good for voltage-wise but its a foot long and has creepage disks near the handle so it is good enough for this.

Looking at the voltages, they all seem close enough. One thing is that the line going to the CRT plate (pin 7) has an RF choke and it appears to be inline under some plastic tubing. It looks like it may have gotten hot. And the contact was corroded, did what I could for it.

Another thing, I had to substitute 3*1200pF caps in parallel for a 3900pF for C42. The idiot that does the ordering around here (me) screwed up and ordered 0.039 instead. Don't think that would make much of a difference though.

So, I am leaning towards a weak picture tube. I am going to have to buy a tester, maybe I'll go post a want in the classifieds.

Here is a shot of Peter Gunn.

Jonathan

Probably is a weak CRT.

Good luck.

It's got the classic 'silvery' look of a very weak jug.

:tears:

OK, in the absence of a CRT tester/rejuvenater, I am looking at options for trying to wake this tube up.

1) In circuit, reduce the ballast resistor value, either by replacing one of the sections with a lower value or putting a variable power resistor in parallel. Check the voltage delivered with the CRT filament out of circuit and a 3.9 ohm resistor subbed in. Target voltage 2.34 volts * 1.4 = 3.22 volts. 5-25 minutes. Questions: Video signal or no video signal during rejuve? After rejuve, increase nominal filament voltage by about 15% (2.8V) as with a tube brightener?

2) Make a rejuvenator like one of these two, one is a link, the other a PDF attached. While similar, both have some differences. I have the stuff for either. Seems like it is a more of a real rejuvenation as opposed to just upping the filament voltage.

http://www.thevalvepage.com/teletech/crt_rej/crt_rej.htm

I'm thinking the answer likely is to try #1 before moving on to #2. It would be real nice if I could get some life out of this tube.

Thanks for the help!

JOnathan

Keep in mind that all the filaments are in series. Lowering the ballast will increase the current through all the tubes and the voltage will be split between them in the same ratio as before. There will be very little increase in the CRT voltage.

Video signal makes no difference. I've found that if a CRT is going to wake up, it will do so even at it's normal operating voltage, it just takes a while longer than using elevated voltages.

Rejuvination works by blasting a layer off the cathode. There's not much material there to begin with in these short necked CRTs and it's liable to make things worse.

I hate to say it, but I've encountered about a dozen of these 21EAP4 CRTs and all were deep into the bad. No waking up or rejuvinating helped :(

Duh on the series resistor. Then why did Philco say to bypass part of the ballast resistor for the 6.3V tubes?

OK. So I might as well try an external rejuv circuit, what have I got to lose? Opinions on which circuit or techniques to use in a last ditch effort?

On the next expedient. I do have a 21FAP4 NIB. In other threads the thought was that this tube should work but nobody had yet, at least as far as I could see. Looking at the data sheets, it seems the main difference is that the 21EAP4 has an extra grid tied to the anode. And that G1 and G2 pins are swapped and that G3 on the 21FAP4 is the same as G4 on the 21EAP4. So does all of that boil down to swapping G2 & G3 on the CRT socket?

Thanks!

Jonathan

After thought: What about putting a 3.9 ohm resistor in place of the CRT filament and then making a separate power supply for the CRT filament?

The 6.3 volt CRT has a higher filament resistance. If you don't bypass part of the ballast, the current through all the tubes will be slightly reduced. So slightly I doubt any difference would be noticed. In fact it will prolong the life of the tubes to run them a little on the lean side.

Although I haven't tried a 21FAP4, I picked up to of them with the intent of using them in Predictas. I don't see any reason why they wouldn't work very well. I'm, not sure about the socket rewiring.

Sure, you could power the CRT filament separately if you want.

Really shameful how poorly I think things through. Duh again. So Bob, do you agree that swapping the two pins (2&3) on the crt socket?

Still going to try some rejuve on the 21EPA4 and still looking for opinions on the best way to go about it.

Thanks!

JOnathan

I have an old Heathkit CRT tester/rejuvenator that works like the circuit in the PDF. It does a very good job. I agree you have nothing to loose so I would try it.

So, built up a quick and dirty variable power supply based on a LM317. Driving the filament close to 3V provides a much brighter picture. However, it is really washed out and the contrast doesn't seem to be working although the brightness does. Is there anything other than a weak CRT that can cause the washout? Any ideas why the contrast isn't working when it was before? My DMM finally crapped out, bringing experimentation to an end for the evening. I ordered another but I am headed to work until Wednesday anyway.

I hope to have enough time to build a rejuvenator this week but it is going to be a busy one.

Thanks!

Jonathan

Not getting much time in this week. Got my new meter (Fluke 117). I fired the set up and noticed that the video output tube (6AW8A) is getting hot with a dull red plate. I don't believe it was like that previously. Looking at the voltage:

Pin 9 = -30 (negative 30?!, SHOULD BE +190v)
pin 8 = 180 (should be 140)
Pin 6 = 1.5, should be 1.2V

Haven't had time to check all the resistances. Any quick suspects?

Jonathan

Well. Things just took a sour turn.

As noted above, the video output tube looked like it was running hot and had a very wrong voltage on pin 9. Doing resistance tests showed a problem between the 280V source and the main PCB. I discovered that R33, a 3.9k resistor had very high resistance. I swear I checked and it passed when I was under the chassis. Replaced it, got good voltages and the best picture I have had. Not great by any means but better. While I was admiring it, about 10 minutes into the run, smoke and flames erupted from the flyback wires. Sigh. I had been playing with the focus wire that has two possible positions but that's it.

So, now I need a new flyback and to find out what blew the original. As it will be very difficult to find an exact replacement, any suggestions as to something that will work? This isn't a museum restoration, just a set for occasional use.

Argh!

Jonathan

Hmm. Upon taking resistance measurements, the flyback appears to have survived. Could I really be that lucky?!?! I can see a nasty scorch between connection D (wire to the plate of the horiz. output tube) and the flyback frame. Carbon tracking that finally got bad enough? Or excessive plate voltage on the horiz. output tube?

Back to puzzling.

Jonathan

Flyback might have survived. Can you post pics of the damage?

If carbonized phenolic terminal boards, you can scrape it out to get rid of the conductive char layer, and then coat with insulating lacquer. If you need to replace/patch a piece, a sheet of FR-4 epoxy glass laminate works well.

You have to handle that Fly with extreme care though, they are usually so cracked and decayed that the wire from the tire to the rectifier will break right off.

OK, here is a pic. Is it possible that the plate voltage was too high or do y'all think it was a carbon track that built over time and today was it's day? I was getting a brighter, better picture than I had been after replacing the 3.9k. So maybe it was being asked to work for the first time in a long time.

I'm going to start digging and cleaning the board and see how deep it goes. But what can I check before I fire (haha) it back up? I got lucky once, don't want to push my luck.

Thanks for the help!! My blood pressure is returning to normal. :-)

Jonathan

It just arced over, either from dirt or moisture and time.

I'd try to Dremel out the path between the terminal and the frame, you can leave enough of the Phenolic around the terminal to support it but remove all of the charred part.

Lots of hair fine wires on that board so you'll need a steady hand with the Dremel.

That should be repairable using reasonable care. I would consider carefully unsoldering the wires from the lug, removing the lug completely from the phenolic, cleaning up all the carbon, and remounting the lug (or a new eyelet/tie point of some type) on a bit of FR-4 epoxied over the original location.

If your B+ is higher than spec, then the pulse voltage at the HOT cap will be, as well. But that was probably an existing carbonized area that decided to arc over due to dust/contamination or whatever.

http://videokarma.org/attachment.php?attachmentid=192496&d=1474241381

Maybe I'm seeing things, but it almost looks like there was a trail of some material(possibly flux) that ran from the terminal down to the fly frame. Whatever it was it finally carbonized.

Dirt, grime 50 year old Cigarette soot, eventually it gets conductive enough to arc over and then it's too late.

It's often a good idea to clean the HV area on any set, a Q-Tip and some 91% Alcohol will do the trick.

Yeah, I shoulda, woulda, coulda cleaned the HV area. I will next time, I'll tell you that.

Dug up a piece of phenolic and cut out the burnt area. It was pretty big, had to file a 3/16" groove to get rid of all the soot. Then I glued the new piece in on top with the terminal already installed. Thankfully I was able to remove and re-attach the flyback wires without breaking them. Whew! Fired it back up and to my great joy it worked!

Picture is indeed improved. Watched a "Tales of Tomorrow" on it. Pretty good one, actually. Still much improvement needed but it still lives!

Thanks a ton for the help, folks. Once I get a chance to work on it some more I'll have plenty of questions.

Jonathan

Nice repair!

I would shorten that screw a bit, though, to reduce the risk of corona/arcing to the donut in the future. Maybe cover the cut end with a blob of electronic-grade RTV.

Good idea, I will. Should have when I was putting it together but I was too anxious to see if it worked. And some RTV on top sounds about right. Off to work for my 48 hour shift so no work on the set for a couple of days.

Many questions about improving the picture.

It takes at least 5-10 minutes before the picture stabilizes. The horizontal hold is fussy and the picture shifts around. Once warm the horiz. is fine and the shifts are much less but still there.

Even when warm there are faint diagonal lines that are mostly apparent when there is nothing on the screen.

The bottom of the screen is not filled. I'm sure that is just adjusting the picture correctly.

The left side is a little compressed ad the whole screen seems a little blurry.

And early ideas on those issues? I'll get a test pattern downloaded and a screen shot taken of that later this week. I was also planning on subbing tubes one by one and seeing what I get there.

Progress! Talk about a roller coaster ride yesterday. The thrill of victory and the agony of defeat!

Jonathan

Those diagonal lines are called Retrace Lines. They can be caused by two things 1.) driving the electron gun to the circuitry's limit (which is usually done with a weak CRT to make it look better), or 2.) blanking. Blanking is a circuit that feeds pulses from the vertical to the video amp/output or one of the elements of the electron gun...To prevent the gun from writing in the time it takes after the end of the last field for the beam to return to the start point...when the beam does write it creates retrace lines.

Re bottom of screen if you did a full recap, but did not touch the vert size/height and vert linearity controls then try those first...You want a test pattern with evenly spaced horizontal bars. Adjust the set with that pattern so that the space between bars on the sets is even and fills the screen...You may also want/need to adjust the centering rings while doing this.

As for the side being compressed look for horizontal size/lin controls and see if that helps...If minor it could be natural for this set. Some non-linearitys if minor can or should be swept (pun coincidental) under the rug....If the set has a lot of overscan, and the picture is not centered such that more of the bad side is shown changing the centering to move the non-linearity off the screen may be worth doing.

Back home from work. I should be able to get some time in on the set today.

Tom, when you say driving the electron gun to its limits, do you mean having the brightness cranked or upping the CRT filament voltage? Right now I'm running the brightness at 3/4 and the CRT at normal voltage. I'll start looking into the blanking circuit, any troubleshooting tips on that?

Today I will let the set get properly warmed up and try to adjust the picture with the controls to see how good I can get it. Then I want to start digging into why there is no audio. On non hot chassis set I would feed an audio signal into the input of the circuit. With the set on an isolation transformer and the sig. gen. NOT on the iso transformer, can I do it that way?

I have been running the CRT filament from a separate power supply, a 12VAC transformer/rectifier/LM317 setup. This has been handy, it helped wake up the CRT by running the filament at 3V for a few minutes. I'd like to milk what I can out of this CRT and being able to nudge the filament voltage should help. And when I do install my replacement tube I'll be able to easily up the voltage to 6.3V without disturbing the series filament current. I was wondering if I could tap into the series filament string at some point and pick off 6-12VAC so I could ditch the transformer?

Thanks for all the help folks!

Jonathan

The blanking circuit picks a signal off the vertical output, runs it through the K1 couplate applies it to the CRT grid. So it could be the couplate is bad or the CRT is so far gone, the blanking signal isn't effective.

Yes, you hook up the sig gen that way. Only the TV get's plugged into the isolation transformer. Nothing else!

Wire the new CRT filament exactly as the old one was. You don't need to change anything. The resistance in the tube filaments vary with the current running through them. Sort of self regulating. Just try it and you'll see what I mean. The new CRT will have about 6.3 VAC across it without any changes needed.

The limit varies from chassis design to chassis design. Some sets it is over %50 brightness and or contrast, on others it is outside control range. ...On sets where it is not in control range normally, if it dips into range it means the CRT is weak....I've yet to operate a predicta of that era so I can't give you a concrete target.

Well, last week I suddenly stopped getting video. I suspected that it might be the RF modulator I was using so I went and got a small test set to try it on and wound up with four of them. And while the test TV's all had their own issues I could see the same video issue and no sound from all of them, so the modulator is not working correctly. So this morning I finally bought a Blonder Tongue AM60-550A. So when that arrives I can get back to work on the Predicta.

Jonathan

So, it turns out I didn't entirely lose video as I thought. Maybe a loose connection or some sort of operator error. I got an Eico 633 CRT tester/rejuvenator yesterday and hooked it up to my CRT. Some of the leakage and continuity tests were on the edge and the quality test was well into the red and the life test caused a ~50% drop. So, I did the first boost procedure and retested and whaddya know, now on the high end of green and the life test drops it less than 5%! Wowsers. And no, I don't expect it to last forever.

Turned the set on and the pic was indeed brighter! However, everything was color inverted, black was white and white was black. I'm guessing that is my dying modulator, which is indeed having issues. Are there any other causes of color inversion?

Another interesting thing: After rejuvenation, the picture now fills the screen. Any ideas why that would be?

Thanks!

Jonathan

There are several things that can cause inverted luminance....Setting contrast and or AGC too high is one of them. Try minimizing contrast is that still does not fix it note the AGC setting and then try backing it down till the video un-inverts...If you loose signal before then, it indicates there are other problems and in that case it may be worth wile to return AGC to it's previous setting. Personally I would avoid monkeying with it until you have a decent modulator set up.

Agreed. I'm not monkeying with the set until I get the new mod and then try it on one of my tester TV's first. So instead I'm playing with an Eico 147A signal tracer I picked up yesterday. Got it working, so if my audio issue continues after I get the new mod (which I doubt) I'll have tube test gear to track down the problem! I'm using a Heathkit audio generator IG-18 to drive the tracer with. Fun stuff.

OK, I think it's time for a recap on this thread.

I have replaced all the resistors and paper caps on the main PCB. The couplates were replaced with ones made by Bob. Under the chassis I replaced all the paper caps and most of the resistors, I left a few that tested good. K7 is original. The IF and tuner sections have not been touched. My 21EAP4 was/is weak, zapped it with the rejuvenator and it tests well into the green now and passes the life test easily.

Got the new modulator. I'm glad I had the test TV to get it set up correctly with, it took a few minutes to get the sound set right and so on. Hooked it up to the Predicta and I was getting a very unstable picture and no sound still. Since I'm more comfortable with audio, I started trouble shooting that and soon discovered that the 12CA5 looked ugly, I'm surprised I hadn't noticed that already. Checked voltages and the 140V supply was way low. Replaced tube and voltage came up but still no sound. Injecting an audio signal into the 12CA5 did produce a tone. Started working my way back and found a broken wire on the volume pot. Fixed that and still no sound. Disappointed, I was fiddling around with the fine tuning and what do you know, I got sound! The picture is a little unstable, but when it is locked in it is pretty good.

Remaining issues:

I have to tune for not quite the best picture to get sound. Best picture = no sound. The set tunes with the tuning control very close to one end. I see there is an adjustment pot next to the DIP switches on the modulator. Maybe tweak that to get the channel tuning centered? I found a manual for the modulator when at work and can't seem to find it now. I am feeding the signal to the set with coax and a balun, not transmitting and antenna.

When the picture has a lot of white, the sound gets way more buzz.

Horizontal control is unstable. It will lock for a while and then roll, sometimes re-locking, sometimes not. When rolling I get diagonal re-trace lines, sometimes across the entire screen, sometimes just in sections. It's easier to lock the picture when I have it tuned for best picture but then I get no sound.

12CA5 looks like it runs hot to me, it's lit up like a Christmas tree. And that is the socket that had to be replaced and the components around it look like they have been baked.

So many thanks for all of the help! Rio and I watched the set for about 3 hours last night and while the rolling was annoying it was still so much fun to watch. And when the picture is locked in it is more than acceptable. Once I get the dang thing to lock it needs some linearity adjustment, things are a little tall and skinny but not too bad. Really great to see this project start to come together!

Jonathan

On the modulator, sound buzz on white is a symptom of video over-modulation. Feed the modulator a mostly white buzzy image then turn the video level control down till the buzz disappears or is minimized while maintaining decent video.

By the 12CA5 'lit up like a Christmas tree' is it orange glow from the heater perhaps being ran hard, is it blue/purple glow from the tube being gassy, or the plate glowing red/orange? The first may be a problem but is not as bad as the latter 2. If gassy get another tube. If red-plating you have a bias issue that should be corrected immediately....If you run a red-plating tube for more than a minute you may permanently damage/ruin the tube. Deal with this first if it is the latter 2 issues.

Lastly you probably have minor audio alignment drift. Get a set of plastic alignment tools set the fine tune somewhere between best picture and best sound (maintain some sound to know if the adjuster is improving it's level or reducing it), and adjust the sound IF for best sound, walk the fine tuning towards best picture and repeat. Note all adjuster settings and how much you change them so you can return them to original if no change occurs or the problem gets worse. Do NOT touch the video IF adjusters (those require lots of calibrated equipment, skill, and practice to adjust correctly).

You may want to look at voltages in the synch separator and horizontal AFC/osc sections too...Can you flop the horizontal out of synch on either end of the sweet spot? If not (assuming the hold control is a pot) you may want to center the pot and adjust the osc transformer to synch with the pot centered, then re-check.

The modulator adjust is likely for the modulation or output level, not the carrier frequency. There is a slug in the tuner for each channel that can be reached from the front of the tuner. Set the fine tuning in the center of it's rotation and tweak that stations oscillator trimmer. Adjust for best picture then go through the audio alignment procedure outline in the service info. It's all done by ear and pretty simple to do.

Hi All,

Well, not much time to work on the set this week. I did get the audio tuned in better, but it is still weak. A9 makes a little difference and A10 does nothing. A11-12 is blocked by something inside the can, I'll have to look into that.

Fiddling with the tuner adjustment to center the fine tuning knob does very little. As do the vertical and horizontal linearity adjustments. A test pattern looks really bad and adjustments seem to make very little difference. On the good side, putting the HV cage back on and swapping the sync seperator tube seems to improve the roll and retrace lines a little.

Off for my 48 hour shift, should have a little time to play with the set this week.

JOnathan

The tuner adjustment should have a profound effect as it changes the local oscillator frequency. There are twelve of them - make sure you're adjusting the correct one for the selected channel. Vertical linearity control should also have a large effect. There is no horizontal linearity control or do you mean the "T" bar magnet inside the CRT housing ?

Hi All,

Whew! Busy fricken' week here! Not much time in on the Predicta this week but I do have 40 gallons of apple cider fermenting!

The thing blocking the A11-12 audio adjustments turned out to be part of the slug is broken off. Crap. What are the chances of a repair? Or should I just start looking for a replacement? I'm still having trouble getting good sound with no 60 Hz hum. The buzz control doesn't affect the hum at all. It is driving me crazy and is the biggest thing preventing watching the set being fun. Maybe C34? Or some other ceramic cap?

On the upper 1/4 to 1/2 of the screen is (sometimes) a whiter area. It moves with contrast/brightness changes in whatever you are watching. If the scene is darker it disappears.

The vertical linearity control does nothing. Neither do the vert centering or horiz centering up on the CRT.

And a bonus non-electronic question: Ordered the Novus polish. Do y'all hand polish or use a small buffing wheel? I may have to break out some sandpaper for some scratches.

Thanks and sorry for it being so long since I updated the thread.

Jonathan

EDIT: Forgot to add that cleaning the tube sockets and pins in the tuner seems to have resolved the horizontal hold issue, it is locked in quite well now. Is it likely cleaning the sockets was the fix?

And a bonus non-electronic question: Ordered the Novus polish. Do y'all hand polish or use a small buffing wheel? I may have to break out some sandpaper for some scratches.
I hand polish. I've heard horror stories in the past of melting plastic using a buffing wheel.

.

I hand polish too. All those controls should definitely be having a noticeable effect.

Buzz control might not be working because the alignment is throw off by the damaged slug. I suppose the slug could be replaced but finding one with the correct characteristics could be tough.

The centering controls are actually magnets. Unless they lost their magnetism, they should be moving the image around when you rotate them.

If it uses a Zenith style sound demod with a 6BN6 you may want to double check that circuit if the control has absolutely no effect...If it does not vary the level of hum in some way there may be other issues at play.

The buzz control does have some effect. It varies the volume and only in a small range is the audio loud enough to hear and it does eem to affect some buzz. It does use a 3BN6 for audio demod. But the problematic hum sounds like 60/120Hz hum, like it had bad electrolytics on the power side or something. Although I do have to slightly off-tune the fine tuning to get sound, so maybe if it was all aligned correctly the hum would disappear. Any other causes of hum to look for?

Think there is any chance of gluing the core of the broken slug in the audio to a diddle stick? I only need to adjust it one more time. Although the slug is probably stuck, which in turn is why it got broken. Sigh. Anybody got a replacement transformer?

Jonathan

Hi All,

Got a chance to poke around a bit on the set. The vert/horz centering adjustments do indeed work, I was spinning the shaft of the magnet, not the magnet itself! Duh. I have the picture nicely centered now. The vertical linearity definetely doesn't work. Just to confirm, the vert. lin. is the inner of the top (brightness) pot. The pot only has one wire coming to it, to the center contact. The center contact has about .2 ohms resistance to chassis ground. One side of the pot adjusts fairly smoothly from 3 to 1200 ohms or so and then goes infinite in the last bit of the turn. The other side goes from about 1.8 ohms to to 300 or so, then jumps up into the kOhms and gets worse from there. Measuring the resistance at pin nine of V9 I get 296 ohms and it doesn't vary when the pot is turned. So a bad pot. What I don't understand is why it only has one wire connected to it. The schematic clearly shows one side goes to R58 and the wiper to ground. If I understood how it is connected I could sub in a 1k pot to test while I look for a pot. I didn't have the time to disconnect everything to the set so I could look underneath and follow the one wire that is connected to the pot.

Didn't dig into the hum issue but did notice that it does vary with the volume and is there with no signal applied. The electrolytics have been replaced, of course. Later I will ground the control grid of the 12CA5 and see if it persists. If I can get the vert. lin. and hum issues resolved I'm going to call this set done.

Thanks!

Jonathan

I suspect one side of the linearity pot is grounded and R58 is going to the center contact. It makes no difference if the wiper is grounded and one leg goes to R58 or vice versa.

Well, both sides of the pot show resistance to ground that varies with adjustment and the center tap shows very low resistance to ground. There is no connection on either side. Later today I'll disconnect everything so I can flip the set over and follow the center tap wire.

If you have a tube tester look for heater cathode shorts in the tubes and try substituting tubes in the audio and audio IF....A HK short anywhere could add hum, and some tubes without a HK short seem prone to picking up hum from nowhere (I have a 12AX7 like that).

I think that R-58(270 ohm 3 watt) cold end is connected to ground. The pot may have failed and that was a work around for as a replacement pot was not to be found. It is always great to have a factory part. If you can't find a factory part and are not too fussy about factory look put a different pot on back of chassis till you can locate the correct part. Over the years I have seen that done and have done that a few times myself. All the best,Tom.J

Aha! Figgered it out. The pot must indeed crapped out back in the day. There was a replacement pot installed where the optional UHF tuner would have been if mine had it. It looked factory to my uninformed eye, as the holder was indeed factory.

So, it does affect the vertical linearity. However, as I get close to getting the test pattern round, it starts getting egg shaped. So how it was is about as good a compromise as it gets.

One thing tough about working on your first set: I don't know how good was OK back then, picture quality and sound. So no way of knowing if it is as good as it gets or could be improved.

In other news, I bought another Predicta holiday (blond) and a parts set (holiday mahagony). I swear, I'm not a collector! :-) With luck I should have all the parts I need to keep a set running for a long time.

Jonathan

Linearity, height and centering all interact. Getting vertical right involves having one hand on height one on lin, and occasionally tweaking centering in most sets.

If playing with both controls at once don't give you a good linear raster that fills the screen, try tube substitutions and confirm all resistors in the vertical are within tolerance.

Note: if the horizontal over scan is much greater than the vertical and you want to further increase the vertical to prevent the image from being horizontally stretched, there may not be enough vertical range to match....If that is the case you may want to try to reduce the horizontal size (if no such control exists try H drive, H out/damper tube substitutions for weaker working specimens, or sliding a thin sheet metal copper sleeve between the yoke and the CRT neck) or live with it as is.

Tom,

Thanks, that helps. I am off for my weekly 48hr shift so I won't get a chance to play with it for a few days.

I've been looking for a basic, how to adjust a set kind of thing but haven't really found one. And any recommendations for a book on fixing sets geared towards the set owner instead of serviceman?

Jonathan

I've been looking for a basic, how to adjust a set kind of thing but haven't really found one. And any recommendations for a book on fixing sets geared towards the set owner instead of serviceman?


This is a really good one, IMHO:

https://www.amazon.com/Practical-Handbook-Repairs-workshop-library/dp/0668020571/ref=asap_bc?ie=UTF8

This is a really good one, IMHO:

https://www.amazon.com/Practical-Handbook-Repairs-workshop-library/dp/0668020571/ref=asap_bc?ie=UTF8

I've never seen anyone degauss a monochrome set till seeing the cover of this book just now. I can't think of why to do that on anything other than a color set.:headscrat Looks really bassackwards to me. :screwy: :smoke:

I've never seen anyone degauss a monochrome set till seeing the cover of this book just now. I can't think of why to do that on anything other than a color set.:headscrat Looks really bassackwards to me. :screwy: :smoke:

You still haven't, it is a color set. In the book he is explaining that you do the degaussing to eliminate a tinted picture to obtain the best greyscale image possible on a color TV set. Therefore the color control is turned down.

Page 68 in the book shows him doing the degaussing on the same set, and the set says "color" on the control door below the on/off/volume control.

.

You still haven't, it is a color set. In the book he is explaining that you do the degaussing to eliminate a tinted picture to obtain the best greyscale image possible on a color TV set. Therefore the color control is turned down.

Page 68 in the book shows him doing the degaussing on the same set, and the set says "color" on the control door below the on/off/volume control.

.
That makes a lot more sense. (IIRC I don't have any literature by that author.) I can't recall seeing someone do a degauss without the screen being a primary color or in normal opperation. In my experience only the worst gaussed tubes show it on a monochrome picture, but if you have a primary color raster even the smallest impurities show up clearly....

Jim,

Ordered a copy, $5 delivered. Has to worth at least that! ;-)

Thanks for the suggestion. Anyone else got a favorite site or reference for TV troubleshooting?

Jonathan

Jim,

Ordered a copy, $5 delivered. Has to worth at least that! ;-)

Thanks for the suggestion. Anyone else got a favorite site or reference for TV troubleshooting?

JonathanCan't take credit for that, it was N2IXK's suggestion. I just happened to have a copy of the book handy.

I agree that it was a good suggestion.

.

Oops! Thanks for the correction.

Hi All,

Just not enough time in the day. Anyway, I have gotten a little time in on the set. Rio and I polished the shroud and it came out nicely. We plan to start on the CRT cover this evening.

Got a lick in looking for the nasty hum. I still can't properly adjust the audio alignment due to a busted slug in A10/11. I have bought a parts set and hope to have a replacement soonish, but it will be some weeks before I pick it up. I don't think it is the alignment, you can see the 'scope trace below. It's just a really cheap digital 'scope. Nonetheless, you can see a clear, loud 120Hz signal and a lot of other nastiness. Things I have done and observed:

Volume control varies hum loudness.
Touching the volume pot reduces hum quiet a bit, although it is still there.
Removed the 3BN6 (audio connector) tube and put a 5 ohm resistor across the socket filament. Hum still there.
Connected an extra 100uF cap across the 140V supply. No change.
It's a new 12CA5. Don't have another at the moment. Old one is gassy and dead.
Cried, whined and complained. Didn't help, no change.

I gotta figure this out. While the picture still needs quite a bit of work, the set is still fun to watch. But the hum SUCKS!

Thanks!

Jonathan

Try turning the vert. hold control fully stop-to-stop and see if the hum (or buzz) changes pitch.

OC, without the CRT connected it makes no difference. With the CRT connected, IIRC, there is a high pitch whine at either end but not sure what the hum does. I can reconnect the CRT and and see if needed.

The idea was just to see if the hum might be vert sweep bleeding into the audio. But since the pitch doesn't change with varying the vert sweep rate, that's not the source of the hum.

I'd recommend getting 3 examples of each of the audio tubes to try substitutions. Scope around. If it is not the tube it's self making the hum it must be on a PS rail or one of the pins feeding the tube.

Tom, the noise persisted when I pulled the audio detector tube and put a resistor in-line for the series filament. So I *think* that pretty much confines it to the audio amplification stage and power supply.

My Tek 'scope is failing and I am too chicken to put my digital 'scope on the power supply. My gut tells me that is where it is but the caps are all new, so what else could it be?

It could be the tube it's self...I've seen tubes that just liked to pickup and amplify hum even when all sources in circuit had been killed (heaters running on regulated DC, B+ clean and regulated, shielding added, etc, etc).

I don't have the schematic, but suspect that the set may use a 'stacked' audio output stage (that's where the output tube does double duty, serving as a big fat dropping resistor supplying B+ to the IF strip etc. Maybe someone could post a pic of the audio section schematic. There may be something wonky with the voltages on the output stage.

Just on the way out the door for my 48 hour workday. I couldn't quickly figure out how to get just the audio section of the set, so here is a link to the whole thing:

www.earlytelevision.org/pdf/Philco_G4242-Predicta-Holiday-Sams-439-1.pdf

I don't have a second 12CA5 ATM. If I had known the one I had was dead, I would have gotten a second. I'll place a tube order soon. But until then I'd like to keep running down other possibilities. I also tried moving wires around, especially the ones that go to the volume pot and back, no joy. So probably not noise being coupled in.

Thanks folks!

Howdy Folks,

Been playing with the Predicta a bit and have discovered a few things. Firstly, a lot of the noise was because I have to drive the video modulation and signal pretty hard to get the set to show a good picture. I'm guessing that is because I haven't touched the IF and the tuner circuits yet. However, careful tweaking of everyting has yielded decent audio with totally acceptable hum. I also put a .1 cap from the volume pot body to ground, which helped quite a bit. The volume is a little low but OK. Remember that I can't adjust A11-12 because of a broken slug. I do have a parts chassis coming something soon. The volume pot is supposed to be 2.5 megs and is actually 3.5 megs. I wouldn't think that was a big deal, but is it?

So, on to today's questions: If I replace the resistors in the tuner section, am I likely to throw the alignment way off? I don't want to mess with IF alignment, even though I may have the tools to do it. So if replacing the parts will likely mess up the alignment I'll leave it as it is.

One thing I have noticed is that the scan lines are thicker at the bottom than at the top. What causes this?

Oh, and got the book. Looks good, should get a chance to really read it this week.

Thanks!

Unless resistors have drifted high AND out of tolerance it is best to leave them be.

Your discussion of audio and video levels being high on the modulator to be right on the set bothers me. If the audio and video LEDs on the modulator are lighting then you are running it at over modulation (which causes audio buzz/hum). What you should do is adjust the modulator to NOT over-modulate/look right on a modern analog set, then adjust the AGC on the Predicta for sufficient contrast or max contrast before over-drive/sync tearing/negative video occur (ie make it bad then back off a bit till it is good again).

Scan line size is a function of vertical linearity. Have you adjusted the vertical with a grid test pattern yet?

Tom, the only AGC adjustment on the Predicta is the local/distance switch on the back and I have played with it quite a bit. I can get a decent picture with either setting but with different settings. I am using the one that allows the lowest contrast and brightness. Is there anything else I can do? I understand not wanting to over modulate and have it set just so I see some occasional flashing of the LEDs. If I adjust it any lower the picture gets poor and the sound volume too low.

As to a modern set, my little RCA AC/DC doesn't seem to be doing all that well. I may have to dig into that or see if there are any newer sets at the thrift stores in town.

So to make sure I understand, should I go through the tuner and IF and check all the resistors, replacing only those out of spec? And if I do so, will I need to re-align? And are there places that can align if I send them the board? I do have a sweep/marker generator, untested, and a 'scope. But I have never aligned a set and am aware that it takes skill as well as tools.

Thanks!

You might potentially achieve auxilary AGC by varying the RF output of the modulator.

Replacing only the off tolerance resistors might restore proper alignment or ruin it...It depends if the last alignment was with those resistors in proper tolerance. If so (likely), then it should help bring it into alignment. I'd stick to only the off tolerance units to avoid unnecessary changes.

It is possible there might be a service to align it for you...I've never looked for or used one so I can't help you with that.

Also be aware that these sets were never meant to equal a modern SS CRT set in picture, so knowing where to stop fixing it is important.

Hi All,

Been taking a break from the Predicta for a couple of weeks. I needed a break and I had a couple of ham radios on the bench for other folks that I needed to get to. In the meantime I managed to pick up the parts set and complete set that I bought a few weeks ago.

Luckily, the parts chassis has an A11/12 that appears good. Didn't ohm it yet but the slug is intact and moves. So, I plan to remove it and install it tomorrow. Since I have to take the PCB off again, I am wondering if I should remove and test the ceramic caps. I now have a Heathkit C3 capacitor checker, which I did not have the last time I had the PCB off. I would like to track down any problems that might be the cause of the vertical linearity and horizontal hold issues I am having. Any thoughts on that? Any particular culprits to look at?

Got the A11-12 tuning can off the parts set. I see that there is a slug that is only accessible from the bottom. I am assuming that is adjusted at the factory and only the top slug needs to be adjusted on the set. Is this correct?

While I have the PCB off again, I want to look for anything I can do while it is off. I checked C43, as I have read it can be a problem and is the only mica cap on the board. It tests fine, in the ballpark for capacitance. I leak tested it to 450V, which is as high as I can go. Should that be enough of a test?

And again anything else I can look at? My remaining issues are poor vertical linearity and troble locking the horizontal hold. One thing I should note is that I didn't have the correct value cap for C42. It is supposed to be a .0039. What I had on hand was three .0012 that I put in parallel for .0036. Think that should be ok?

Thanks!

RE: the slugs are they Hex like allen keys or are they screw driver adjustments? If hex then you need the correct alignment tool to access both from the top....They made plastic hex diddle sticks that had a hex end with a shaft above it thinner than the hex so you could push the hex clean through the top slug then into the bottom one.

Without a schematic to see the use and spec of those caps I can't really advise you much. Sweep stage caps can see high voltage spikes (which tends to kill sweep micas) and may be hard to fully test. If your tester is only able to leakage test below the rated voltage of a cap, and that cap is a likely culprit, then just change it. I've seen caps that only leak above a certain voltage....If you can't test to rated voltage only assume good if the circuit works.

My recollection is that the top slug and the bottom are the same diameter. I'm at work for 48 hours so I'll look when I get back. They might be different diameters. If they are the same, I think it must be set at the factory. In the Sam's it only mentions tuning one slug in it, although it is a pretty generic "tune for best audio" kind of thing.

I can order a new cap for the sweep mica. Or I may try ginning up a ~ 1kV test supply. I have some HV transformers I could run with a variac. What are the symptoms of a bad sweep cap?

Jonathan

My recollection is that the top slug and the bottom are the same diameter. I'm at work for 48 hours so I'll look when I get back. They might be different diameters. If they are the same, I think it must be set at the factory. In the Sam's it only mentions tuning one slug in it, although it is a pretty generic "tune for best audio" kind of thing.

I can order a new cap for the sweep mica. Or I may try ginning up a ~ 1kV test supply. I have some HV transformers I could run with a variac. What are the symptoms of a bad sweep cap?

Jonathan

I was not trying to say the slugs are different diameter I was describing the taper of the diddle stick on the diameter..... The slugs should either have a hex shaped doughnut hole all the way through in the middle (which would allow both to be adjusted from the top with the correct diddle stick) OR have a solid center core with a groove in the top for a flat head blade screw driver to adjust them (the blade style will NOT allow both slugs to be tweaked from the top).

Your Horizontal and Vertical sweep stages have many caps doing many different things (and interact with most other stages in some way), depending on which cap fails a VAST plethora of symptoms could result.

Show us which caps or which symptoms and probability/nature of cause and effect can be assessed.

Hmm, the post I made yesterday seems to be gone.

Tom, I didn't get what you said and posted a question up on ARF. Sometimes I feel bad pestering everyone here and try to spread out the pain.

I get it now, a diddle stick that allows you to reach the bottom from the top, with a thinner section to go through the top slug.

All the paper caps have been replaced. I will replace the mica cap or kludge up a ~ 1kV power supply to test this one properly. Current symptoms are:

Poor vertical linearity. A test pattern is egg shaped at best. The scan lines are thicker at the bottom than at the top.

Horizontal hold has trouble locking. It will lock for a while then roll. Part of this may be that I have had to off-tune some to get audio, so hopefully once I get the audio aligned correctly that will be less of an issue.

Thanks!

Non-linearity could be caused by the mica caps...In sets like these and older ones with older parts changing the sweep micas is very advisable.

As for the horizontal hold focus on the Synch Separator circuit and the area around the Horizontal AFC diodes (if those diodes are not tube then they should be replaced).

There is only one mica cap in the whole set and it's the 390pF mentioned above in the horizontal multivibrator oscillator. The AFC diodes are in the 9BR7 tube.

Make sure that replacement vertical linearity control is indeed 1K and check the 390 ohm 3W resistor in series with it. Also try swapping out the 10DE7 vertical output tube.

Also make sure the 200uF cathode bypass on the vertical output tube is good.

Digging through my mica caps I don't have a 390pF, but I do have two 150pF and two 50pF that measure out at 396pF. I would have to wait a week to get anything ordered and I am dying to see if the new A11/12 audio adjustment works. Is it electronically foolish to use the four cap combo? I don't care about style points and I'm going to order a few anyway and I'm sure I'll have the PCB off again or can take it off.

The Sams for my set shows and has a 270 ohm, 3 watt resistor. It does go to the vert. lin. pot. As it happens, that is one of the few resistors that I left the old one in place as it tested good. I think I'll peel that one out and replace it.

The vert. lin. pot measure 900 ohms, works smoothly. I will swap the tubes again. I did before but so much has been done and I'm not sure when I tried it in the process.

I feel like I'm getting close. Thanks for all the help!

EDIT: I forgot to ask, if ordering a new mica cap, is it worth it to get a N0 cap?

Sorry, I meant 270 ohm resistor, not 390 :o

Four caps together should be OK but you may introduce some stray inductance and noise pickup if the leads are long.

I'm not sure what you mean by N0 cap ? A standard 5% 500v mica cap is fine.

Well, woohoo! Put it back together with the mica cap combo. Aligned the sound and it sounds great! I had removed and cleaned the buzz pot and that seemed to help a lot. Horizontal hold locked in! Scan lines are much closer to the same side top and bottom. Pretty cool. The vertical linearity is the same though. If this is as good as it gets, I'm happy and I think I can squeeze out some more.

I'm using a 6.3V CRT and the yoke that came with it was damaged a little, the housing partially apart. I can see that a straight line across the screen horizontally dips down on the left and up on the right. I'll see if I can kid it into shape and if not I'll put on the one that came with the set. I haven't really tried to tweak it all in yet, but I will. I'm kinda scared to touch it, it's working so well.

Many thanks! Progress!

Cool! I'm glad the new coil worked out :thmbsp:

OK, now I want to get after the vertical linearity. Swapping out the 10DE7 has no effect. The 200uF cap is new. What else can be affecting the vert.lin.?

I wonder if it is just that I don't have all the controls adjusted correctly. I'm sure there must be a proper order and method to adjust everything but I don't seem to be able to find much information. Anyone have any guidance on this?

Once I get the vert. lin. straightened out it's on to other restoration aspects. Naturally I have a bunch of questions! First is: The HV wire to the CRT. It's old and stiff and has a couple of cracks in the outer insulation. Should it be replaced? I do have some neon sign wire around here somewhere or could buy something appropriate. I do hear some sizzle and smell a little ozone up at the CRT, is it worth it to figure out some kind of cup as later sets have?

Once I get the vert. lin. straightened outHave you ever looked at the centering widgets on the yoke? There's a diagram in Sams that points to them. On one of my Predictas, the centering was way off, making it harder to get correct linearity. The misadjustment might have been the result of a past repairman trying to compensate for an aging component. Can't hurt to check, anyhow.

Phil Nelson
Phil's Old Radios
http://antiqueradio.org/index.html

I generally put up a crosshatch pattern and jump between the Height, lin and centering till I have a reasonably linear centered-ish picture. Compromise and incremental improvement can be the name of the game if it don't just fall into adjustment.

If the tube is good, generally resistors and caps are next, a check of the B+ and b+ Boost rail voltages feeding the circuit, and last the transformer and yoke.

For HV wire on normal sets I just find a big-screen 90's or newer CRT set at the curb, cut the donor set's HV lead at the fly, and unhook the cup from the CRT....That way I've got the lead and connector together.
Does your set have some kind of HV plug on the flyback end?...If so it could be difficult to properly change the HV lead without causing new problems.

Been doing some playing and, of course, have more questions! First, foremost and very embarrassing but:

I think I may have thought of horizontal and vertical hold backwards my entire life. It would make sense with other learning disabilities I have. I have always thought that vertical hold when you adjust it the picture goes diagonally to left or right until you get the hold correct and then it is straight up and down and that horizontal hold is when the picture flips up or down. You know, the classic, common problem where the picture is part way down the screen and you see a bar at the top or bottom across the screen and when you get it adjusted right the bars disappear off screen. However looking at the way the controls on my set are wired and labeled, I must have that backwards. Straighten me out here! If that is the case, while I do have some height issues, vertical hold is my issue, not horizontal.

I swapped out yokes yesterday. One yoke is from my original set and the other from one of the parts set I picked up. The original gives a more egg shaped test pattern and is harder to lock in the vertical? hold. The other is damaged, has a crack in the housing and even a crack in the ferrite but gives a more oval test pattern and seems easier to lock in. It also affects a straight line across the screen, making it dip up a little on the right and down a little on the right, only near the edge of the screen. This effect is more pronounced at the top and bottom of the screen, meaning a straight line in the middle has very little of this effect but a line near the top or bottom does. There are a couple of HV ceramic caps on the yokes, might these be responsible for issues?

Thanks!

Vertical hold misadjusted results in horizontal black bar scrolling vertically. Horizontal hold misadjusted results in diagonal black bars.

The yoke and or the caps in it may be bad. No harm in swapping either.

Well, as my Pappy always said, if brains were lard I couldn't grease too big a pan. I do actually have a little dyslexia/disgraphia so I'm not too surprised. And while it must be tough answering stupid questions like that imagine what it's like to be me.

So, pulled apart both of the yolks I have handy. Both measured about the same resistance on all the coils. Quite a bit of corrosion in both of them, it looks like the plastic disc that seperates the magnets from the housing is off gassing or something, both have yellow/white substance all over the place and a lot of corrosion on the metal disc. I noticed that the two yokes have different windings, one is larger than the other and may be a different guage. Just in case I replaced the resistors on the one I am using. There was a springy wire on the yoke that was on the CRT that I am using, the other had a wire to a paper that was under the CRT holder. So I made a reasonable facsimile and put that on. I also noticed that the horizontal linearity magnet was a little cocked and straightened that.

It's locking OK and is less egg shaped. What is the proper way to adjust the horiz. lin. magnet? In and out from the CRT but keep it even I assume?

Thanks!

Ok, quick question: I replaced the HV lead to the CRT with a new piece of 20kV, 22AWG wire. I cleaned the contact on the CRT and hooked it all up. I have WORSE hissing than before and visible corona. I checked the HV output and it is 12.5kV or so. What gives? It's making me nervous and I can smell ozone.

Where is the corona, exactly?

Phil Nelson

Up on the crt where the hv lead connects. It is primarily on the edge of the metal ring embedded in the tube. I did clean the area well, both for good electrical contact and then the entire area around the contact for soot and grime.

Thanks!

Well, no good deed goes unpunished. I was putting the Predicta back together. It's been working pretty well, occasional vertical lock issue but only every once in a while. Just before stuffing it all back in the cabinet I checked it, working fine. Tucked it all in, put on the knobs, screwed it all down and wah wah wah....

Now I get a raster, sound but no pic. Tube troubleshooting guide says V4 and V14. Replaced V4, same issue. I bloody well better not be V14 (the CRT). I poked and prodded, unplugged and replugged, looked at tube sockets and I just can't see anything amiss or find anything loose. Gotta admit I was a little frustrated. Any suggestions?

Got scope? Look for a video waveform of appropriate amplitude at the CRT and work back to point of signal origin...It's probably something simple, easy and stupid.

Make sure you plugged the CRT video wire back onto the right post.

Are you running it with the 21FAP4 ? Were you able to resolve the issues you were having with it ?

I do have a scope, a Tek 465M but it has been acting up. I'll try putting it on there and see what I see. If I can get it done before I take off for my 48 hour shift I will.

I did check that the CRT video wire is connected to the right place and I do get a raster. This is with the 21FDP4 I got with a parts set that has been working pretty well. I have not yet resolved the issues with the FAP4, I had to clear off some bench space to work on a couple of things. Any ideas on that one Bob?

You would get a raster even with the video wire disconnected. The signal on that wire modulates the brightness.

I'm wondering if socket was wired right for the 21FAP4. I see that you swapped pins 2 and 3 however.

The 21FDP4 has G1 on pin 3 and G2 on pin 6.

21FAP4 has G1 on pin 2 and G2 on pin 3

So you maybe needed to swap pins 3 and 6 rather than 2 and 3 ?

Hmm. I get no raster with the video wire disconnected, just snow.

However, I have found the problem, it is with the video source. Fooling around with the DVD player got me a picture again. I think my BT modulator may be having issues, even with the video modulation cranked I don't get the over mod led lighting up. I'll have to dig into that. I did briefly hook my scope up to the video output and do get a somewhat similar to the Sam's waveform but it is jittering around too much to get a good look at. I may get bold and try to hook up my little digital scope when I get home from work Wednesday.

Thanks!

Bob, if I needed to swap pins 3&6 instead of 2&3 would I still get a correctly oriented picture? What I get looks right but is dim and weak with retrace lines.

Raster means you have vertical and horizontal deflection. Nothing to do with snow or a blank screen. Glad you got it sorted out :thmbsp:

Yes, you could very well get problems you describe if incorrect voltages were applied to G1 and G2 or if they were left floating.

G1 has the retrace blanking signal and G2 is the electrostatic focus voltage.

Once again I misunderstand basic terms. I'll get there...

Boy, am I glad to hear there is still hope for the 21FAP4. So:

As noted, I swapped pins 2&3. Looking at the 21FAP4 data sheet it says pin 6 is I.C. I read that as not connected. On the 21EAP4 both pins 2 and 6 are connected to G2. I am using a CRT socket and harness from a set with a 21EAP4 and it works fine with a 21FDP4. So, if I am getting this, I can't swap pins 3&6.

As I sit here at work away from the set, now I wonder: Does the CRT connector use pin 6 or 2 for the G2 connection? Maybe I need to change that or jumper pin 2&6? Man, wish I could look at that right now...

I'm not suggesting you connect anything to pin 6 for the 21FAP4. You say you have a 21FDP4 in there now. Take a look at the data for it. It shows G2 as pin 6. So try switching the wire on pin 6 to pin 3 and the wire on pin 2 to pin 3.

So try switching the wire on pin 6 to pin 3 and the wire on pin 2 to pin 3.

Thanks for your patience Bob. But the way I read the above I would be putting two wires to pin 3. Did you mean swap pin 6 to 3 and pin 3 to pin 2?

I believe he is discussing purely pin swaps. Compare the two base pin outs (side by side preferably) of the data sheets below (it ain't rocket surgery). If it originally had one tube in it and now has the other then you need to swap wires so that the one wired in the set's chassis for G2 goes to the G2 (G2=Grid2) pin on the tube you have in there now. You will need to confirm G1, K(cathode), and possibly others.

https://frank.pocnet.net/sheets/168/2/21FAP4.pdf
https://frank.pocnet.net/sheets/049/2/21FDP4.pdf

If you connected your car battery backwards would you expect your car to work? The pin outs of the 2 tubes are different so the socket wires have to be swapped until they match the pin out of the tube you have in there.

Thanks for your patience Bob. But the way I read the above I would be putting two wires to pin 3. Did you mean swap pin 6 to 3 and pin 3 to pin 2?

Yeah sorry. Pin 3 to pin 2. As Tom said, carefully check the wiring and make sure it is correct when you have the 21FAP4 installed.

Don't ever ever just swap.

Trace out the wires to their source and connect up according to the
data sheet of the new tube.

Paranoia in this business is usually the best policy. Knocking on
wood is good too.

I can hear the frustration and I'm sorry for being thick. Sadly, tat is exactly what I was trying to do and I did indeed compare the sheets. I think I may have found the problem and will verify when I get home, but what I think is this:

One does indeed need to swap 2&3 as I did. The 21EAP4 (the data sheet I was comparing to) shows G2 on both pins 2&6 and the 21FAP4 shows it on 2 only and pin 6 is I.C.. I'm guessing that the socket has G2 wired to pin 2 and nothing to pin 6. I'll look when I get home.h

OK, back home and had a little time last night to play. I think where I went wrong with the 21FAP4 was that I didn't check which pin they were using for G2. On the 21EAP4 you can use either as both are connected to G2. I assumed (and we know what that makes me!) that they used pin 2 on the CRT socket but in fact they used pin 6. So a straight wire swap won't work, one needs physically move the wire to pin 2.

So, what I did was remove the two rivets that hold the disc that keeps the contacts in place in the socket. Now I can mix and match locations at will. I have some #4 brass bolts that fit nicely to put it back together. Sadly, real life prevents me from doing it today but I will tomorrow.

Some related questions: The last time I tested the FAP4 I just had it loose, no holder on it. How stupid is that? I was reading that part of the holders job is to prevent flying shards in case of an implosion. I was wearing eye protection and did drape a towel over it when moving it around. Since I am pretty sure the tube is good, I was thinking of putting the holder from my 21EAP4 on it but the idea of doing that puckers me up. How does one tension it correctly so that expansion and contraction don't make it go boom? There is the perimeter strap and the two straps that go around the back. Which order should I attach the straps? Any tips on this would be much appreciated.

I really appreciated the patience and help guys. I know I'm a little thick but I really am trying to learn how it all works.

What we were getting at is that you've got a 21FDP4 installed in your set so forget about the 21EAP4 datasheet. The FDP4 shows no connection on pin 2 so it had to be using pin 6. I bet your FAP4 will perform like a champ when you get it wired up right.

By holder I assume you mean the safety plastic screen cover ? Yeah, it is there for implosion protection. Now I can't be irresponsible and tell there is zero risk, but I think we've all routinely ignored it. Personally, Ive got a couple dozen loose CRTs lying around in and out of of shipping boxes.

As for the band, I make a note of how tight it is before I take it off and try to get it the same when the new CRT is installed. Maybe mark the bolt with a sharpie. As I recall the straps all go one as one piece ? I only loosen the bolts on either side of the band that goes around the face of the CRT and slip the CRT out.

https://c6.staticflickr.com/2/1482/25943280781_24c7493e01_z.jpg (https://flic.kr/p/Fww6wv)2016-03-23 002 (https://flic.kr/p/Fww6wv)

Yeah, I got confused between the data sheets and whatnot. Wrote it all out and drew a diagram and I think I have it now. Taking the retaining disc off the socket will make it easy to get it wired right. Wish I could do it today, I really want to know!

By holder I meant the straps and bands, not the plastic face. Marking the bolts with a sharpie sounds like a great idea. Looking at it again I see what you mean, loosen the perimeter band and I should be able to leave the other two alone and slip the tube out.

Thanks again!

I always go with somewhere a bit beyond snug enough to keep it from being knocked out under the harshest drop that the CRT might survive....If it feels like your crushing the tube with the band then it's time to loosen it a bit.

Expansion/contraction is not much of a concern unless you are keeping it outside or let your thermostat drift a lot.

Marking the bolt on the band while valid can be a bad thing...There was manufacturing tolerance in bulb size (especially from maker to maker), and I've heard of cases of people on tube swaps in other sets doing that and having implosions due to over-tightening to set the band bolts at the same number of turns with a slightly larger CRT.

I tend to slip a screw driver under a gap between band and CRT and carefully/gently pry to see how much give/movement the band has...That gives me a feel for the tension.

Good points. Also, you may have been reading about tension bands offering implosion protection. That is most certainly true of more modern color CRTS but not old B&W CRTs. That band is really there just to hold the CRT in place.

In the event, it was pretty easy to put the bands on. You can tell when you have it right.

And the 21FAP4 is working GREAT!!!! :banana:

As I said above, I removed the rivets that hold the disc on the CRT socket and that allowed me to easily play mix and match. What needed to be done was:

Move pin 3 (G1) to pin 2
Move pin 6 (G2) to pin 3

I can't believe how much better it is. The focus wire actually does something now! I haven't started tweaking it much but the linearity looks better already. Much better detail in credits and stuff with writing. Very, very cool.

I start to think that I might wind up with a good looking, good working Predicta. Been a long road with many mistakes and even a fire but there is hope! Thanks folks, never woulda happened without y'alls help.

EDIT: Guess I better fill in and send the warranty card into Sylvania!!

Merry Christmas all!

Getting in a little time today and I while playing with the focus jumper I noticed that there is 430V instead of 280V on the high side of the jumper. When connected to that I get a crisp picture but the lines are too visible. Looking at the schematic I see it goes to R37 (47K) and then to the 435V boost supply. R37 is in a dotted box, like the couplates. And there are two X's, one on either side of the resistor. What is that all about? Is it possible to use a pot of say 50K to fine tune the focus?

I'll go look into why the voltage is too high. Such a pain to take voltage measurements and whatnot under the chassis of this set.

The x's and dashed lines mean circuit changes, some sets have them some don't. As for the pot, 50K is too small, use a 1meg. min. for a focus pot one end to boost other end to circuit ground center pin to focus lead to CRT. All the best, Tom.J

X means line cut in some models. Dashed means line added in some.

How much vert overscan do you have? More overscan will accentuate the lines. I always tune for sharpest scanlines. You should not notice them from normal viewing distance (Which should be 10'-20' for a set that size). It is not supposed to look good when your face is near the screen...Ever watch a 90's projection set or a 40" color CRT from 5' or closer?...That is the natural look of NTSC when too close to the screen.

Not sure how much vert overscan I have. How do I check?

I am looking at it from far enough away. I can't believe it but I can't find a 1M pot laying around loose. I may see if I can salvage one from some junk. But with 430V on the focus jumper something is wrong. Most likely I wired something wrong under the chassis.

But, with the jumper connected to ground it is too fuzzy, with it floating it is pretty good and when connected to the too hot side it seems like the scan lines are a little too much. I can't believe it but I can't seem to find a 1M pot. I'll get to tracking down the reason for the too high focus voltage.

To measure vertical overscan take a grid test pattern and view it on a LCD and count the bars/squares separating top from bottom, then feed the same pattern into the set and count what you see. If say there is one inch/division on screen and you are missing two evenly then you have one inch overscan on each side (top and bottom that I mean).

You should try to avoid more than 1" of image overscan as it will make the scanlines more spread out and easy to see.

Optimal configuration is to get the scan lines as thin as possible with the focus and get them close together/overlapping with the vertical size/linearity controls (by minimizing overscan). One thing that can accentuate scan lines even when overscan is at minimum is failure of the set to properly interlace on scan I think the term is "double scan" or "line pairing" or something similar (some member had a roundy with that issue years back)....

If you have a lower voltage source than the one you think is too high you can connect a 100k-1M pot at the ends to the two sources, and the center tap to the focus lead.

Didn't have enough time to track down the too high voltage on the focus jumper. In any case I am going to try a pot on the focus and see if I can dial it in just right. I got the CRT protector buffed out and it looks good. I hope to put the set back together this week.

But, before I do I want to go through the adjustments again now that I have a new CRT in the set. I am still unclear on the best order and procedures to do the adjustments. For example, until Tom told me about it above, I didn't know about the vertical over scan. Is there a similar thing for horizontal over scan, adjusted by the width adjuster? Is there a proper order to run through the adjustments?

And the wire wrap connections that are still on the controls, should those be soldered? They look a little suspect even though they seem to work.

Thanks!

Yes there is horizontal over scan which is adjusted with width...If you plan to adjust both do the horizontal first...Many chassis use B+ boost derived from the horizontal to drive the vertical so changes to H can effect V.

Thanks. What do you think about the old wire wrap connections? Seems like a potential source of problems and I am tempted to solder them all.

If undisturbed I usually don't worry. If I unwrap one in the course of work I usually re-wrap a few turns then solder.

So, I got a 1 meg pot and put it on the focus and it works well, nice to have a little more control. I'm working on tracking down the last few bugs. I started looking for a loose connection, if you stamped your foot or tapped the set you got picture issues. Finally tracked it down to a bad solder joint in the tuner connector plug. Must have been loose from the git go. Nice to have that one fixed.

I finished polishing the CRT protector and put it back on. It came out very nice and clear, I used 1500 grit wet sandpaper and Novus 3&2 and spent about three hours on it. I had never actually seen a Predicta playing with the screen cover on. I have to say that while the set looks much better with the shroud and CRT protector on, I wish it wasn't so dark and greenish in tint. Still, the picture looks good and the set looks proper. Putting the shroud on is a mild PITA and I nearly dropped the screen protector!

Over all, I am very happy with the set. There is just one niggling problem and then I can call this set done. The problem centers around vertical hold. Not only does it lose lock sometimes but it jiggles or bounces. I spent some time fooling around with all of the adjustments and got a test pattern looking fairly reasonable but it seemed as if the lock and jiggle were worse. De-tuned the adjustments and it seems a little more stable. Maybe.

Just to recap (rim shot) I have re-capped the set, replaced the couplates with ones made by Bob, swapped out tubes, wiggled tubes and wires. I did replace the mica cap with a four cap combo to get the right value. The CRT is a NOS 21FAP4A and it looks great when it's locked. Raising and lowering input voltage to the set a little makes no difference. I'm running the set at full brightness but the problem is unchanged if I lower it. Contrast seems to have less effect than it used to. If cranked all the way right I get a pulsing flash on the screen accompanied by an audio pulse.

How do I go about troubleshooting this? Help me get this last thing out of the way and I'll get out of y'alls hair! :thmbsp:

Re the vertical sync, try swapping out the sync separator tube. I had experienced some issues on my Barberpole (same chassis) and that cleared it right up!

George

George, I tired that. No joy. It is driving me crazy, this thing would be done!

Went to bed last night feeling defeated. Woke up determined to fight. Since my Tek 465M is failing, I decided to take a chance and hook up my cheap digital scope to the set. I started with taking waveforms 6 through 9, which are appended below, except for W6. W6 calls for grounding pin 7 to ground (chassis, correct?). When I did that the CRT displays a bright horizontal line so it was killing the vertical and the scope was flat lined.

As you can see, W7 and W8 look pretty good. Although if I am reading the schematic they should be at 30hZ and they are at about 60hZ. W9 looks terrible. Could K1 be responsible? That is the one couplate I did not replace.

V9 tube voltages seem close enough:

2 = -19
3 = -19
6 = 115
7 = -7
8 = 11.8

All voltages taken with a modern 10m input meter. The wave forms were taken with the set giving the best picture I can get. The schematic does say they should be taken with 50V PtoP at the CRT. I did not verify that but am going to sneak into the CRT area. Of course I had put the dang shroud back on so it isn't easy. I take it that should be between the chassis and pin 7 of the CRT?

Thanks!

Made a CD with a test pattern yesterday as I had discovered that the DVD player I am using gives a much better picture than the HDMI to composite converter that I have. I'll look into getting a better one. Got the picture tweaked in much better. I can't do the over scan adjustments as Tom suggested exactly as I don't have another set with a composite input. But it is better.

But the jiggle is KILLING me. I've licked all the other problems but can't seem to figure this one out. I have read through and tried the things in the two tv repair books I have.

Here is a link to a video of the problem in action. It varies, there is almost always a little wiggle and then it gets bad and then the picture rolls. Interesting, there are contrast effects that you see through the camera but not with the eye. I apologize in advance for the poor video quality and the ham radio chatter in the background.

https://youtu.be/uTbcTB9KQcY

https://youtu.be/uTbcTB9KQcY"This video is unavailable."

Hmmm. The link works for me. This is the first time I've ever uploaded a video to youtube so I may be doing something wrong.

Been doing some more tinkering. If I crank the video modulation of the BT up to the point where I start hearing over-modulation noise it gets much better. So maybe something in the tuner or IF? Moving the channel selector switch doesn't do it.

So I think I'll go through the tuner and IF tubes again. Last time I went through I wasn't testing looking to see if I could lower the video modulation as I went, I was looking for best picture.

EDIT: Playing with it more, one thing I should have included is that the BT modulator vdeo is well below where the red LED starts to flash but I still get over modulation hum. Right now I have it set to where the hum is bearable and the picture is pretty stable, no rolling and a small amount of hum.

The vertical bounce in your video is sync separator, vertical integrator, or vertical stage related (might also be 60hz line freq leaking into said stages).

Been doing some more tinkering. If I crank the video modulation of the BT up to the point where I start hearing over-modulation noise it gets much better. So maybe something in the tuner or IF? Moving the channel selector switch doesn't do it.
So "it" is the vertical bounce? and the hum/over modulation noise is in the audio, right? How do other working sets do with the same signal?


EDIT: Playing with it more, one thing I should have included is that the BT modulator vdeo is well below where the red LED starts to flash but I still get over modulation hum. Right now I have it set to where the hum is bearable and the picture is pretty stable, no rolling and a small amount of hum.

Some BTs have an 'aural level' control for the sound carrier level that also should be tweaked for best sound (and can cause hum if badly set).

Hmmm. The link works for me. This is the first time I've ever uploaded a video to youtube so I may be doing something wrong.
Just checked now, link works fine. Earlier it acted like a private video.

.

Tom, I don't have another TV to try it with. I should look for a cheapie at the thrift store.

Yes, "it" is the vertical jiggle and the over modulation buzz is in the audio. The red over mod LED is not coming on. The instructions say to crank it until it is flashing red then back off until it only occasionally blinks. If I do that I get way to much buzz to deal with. So I am setting it where the jiggle isn't too bad and the buzz is tolerable.

Duh! I remembered that the LCD screen I use for my computer is actually a TV and to my surprise is does indeed have a cable input. Hooked up the BT modulator and it looks fine and I don't get the over modulation buzz. Didn't have time to really fiddle with it and see how low I could set the modulation and still get a decent picture on the LCD.

So, the question becomes: Why do I get over mod buzz at lower mod levels on the Predicta? I'll puzzle on that while I'm at work for 48 hours.

Have you tried adjusting the buzz control in the Predicta?

Yes. When I had the PCB board off to replace the audio adjustment coil A11/12 I even removed the buzz pot from the board, cleaned and tested it. It makes no difference to the over mod hum. In fact it doesn't seem to do all that much except that there is a sweet spot where the audio volume is the loudest.